Apparatus for automatic measurement of specific filtration resistance and zeta potential of a solid material containing fluid

Abstract: A method is provided to monitor specific filtration resistance in a continuous on-line manner in the paper making process. It can be combined with the simultaneous measurement of streaming potential so as to enable optimization of the chemistry of the papermaking process.

Description: This invention relates in general to the papermaking industry and particularly to an apparatus for the continuous repetition of measurements cycles comprising means for passing a fluid containing solid material to a screen to form a pad of solid material on the screen, pressure regulating means for measuring and maintaining the pressure difference across the pad and screen at a predetermined value, means for measuring the temperature and conductance of the fluid and means for processing the measurements taken. Papermakers have known for a long time that the paper machine is a dynamic changing system. It gives the illusion of being a steady state process but when closely examined from a water quality perspective, the water quality is always slowly changing. The reason for this is long times to equilibrium because of the high residence time recycle loops in the process. A much fundamental understanding exists about retention and drainage on the paper machine but attempts in practical application have been unsuccessful because of the changing system. A fundamental property which is important to retention on the paper machine is the state of the charge on the fiber surface, and a fundamental property important to drainage is specific filtration resistance, hereinafter also referred to as SFR. A laboratory procedure for specific filtration resistance measurement (SFR) under dynamic conditions has been developed and published by E.C. Pires et al in Fluid/Particle Separation Journal, Vol. 2, No. 2 June 1989, pp. 109-114. The trend has been away from laboratory measurements and toward on-line continuous measurements for both drainage and electrostatic charge. Zeta potential is an electrokinetic property of particles suspended in an aqueous medium containing charged ionic species and is an expression of the charge developed on or adjacent to such particles. It has been recognized that the zeta potential of fibrous particles in the feed stock or furnish, used in paper making, has a considerable influence upon the paper produced therefrom.Zeta potential cannot be measured directly; however, it can be calculated from measurements of a related parameter known as streaming potential. A general discussion of zeta potential and its relevance to paper making is provided in "Electrokinetics in Paper Making - a Position Paper" by R.A. Stratton and J.W. Swanson in TAPPI, 64 No. 1, page 79-83 (1981). A survey of various methods of measuring zeta potential, including those reliant upon measurements of streaming potential, is given in an article by H.J. Jacobson et al, in Colloid and Polymer Science 263; 3-24 (1985). From these references, it can be seen that the zeta potential of feed stock or furnish, exiting the head box of a paper making machine, influences the quality of the paper produced by the machine, as a result of its significant effect during paper formation on the wire of the machine. It is known that, in principle, a high particle charge is necessary to ionically stabilize colloidal emulsions or dispersions. There is a mutual repulsion between charged particles of the same polarity which keeps the particles apart and thereby imparts stability to an emulsion or dispersion system. Thus, stable dispersion of clay, calcium carbonate or titanium dioxide can have a charge or zeta potential of -50 to -60 mV. or even higher. Cellulose pulp dispersions typically have a zeta potential in the range of -15 to -20 mV. Cationic charge-neutralizing chemicals such as alum, quaternary amines and wet strength resins, can reduce the zeta potential of a paper making furnish to within the range of 0 to -8 mV. At these low values, the repulsive effect of the charge on the suspended particles is reduced to a negligible value and coagulation is maximized. Conversely, at higher zeta potentials the degree of coagulations is reduced as the repulsive effect is increased. Thus, properties such as first pass retention, formation, drainage, white water consistency and strength can be optimized for a particular type of paper by adjusting the zeta potential of its precursor furnish to an optimum. Early attempts to apply zeta potential technology were often unsuccessful because the system conditions were different by the time the measurement was taken in the laboratory. This difficulty led to the development of the Zeta Data TM on-line streaming potential instrument. It was the first commercially available on-line streaming potential device. In the drainage measurement field a similar evolution has taken place. The standard of the industry to measure drainage is Canadian Standard Freeness (CSF) in North America, or Schopper Riegler Freeness (SR) in Europe. They are empirical tests which measure the drainage time of a fixed volume of a sample. They give a qualitative picture of how a stock drains but no theory exists which can extrapolate their values to drainage on the paper machine. The fundamental measurement which characterizes stock drainage and has a theoretical underpinning is specific filtration resistance. Specific filtration resistance is a property of the slurry and the conditions under which the pad is formed. It is a basic inherent property of material being drained. The idea to use SFR to characterize stock drainage was introduced in the 1950's by Ingmanson and refined into a workable concept by Springer and Pires in 1989. The concept is good enough to be used to predict drainage down a paper machine. With such a parameter as specific filtration resistance available, the paper industry can phase out its dependence on Freeness. The need for on-line Freeness testing was acknowledged in that several companies market such devices which have had significant commercial acceptance. Specific filtration resistance was not used due to industry lack of familiarity with the theory because user friendly apparatus did not exist. There are now several instruments which are commercially available and suitable for the measurement of streaming potential. A method and apparatus for determining streaming potential is disclosed in "Continuous measurements of the streaming Potential on a Paper Machine" by W. Sach in DAS PAPIER 30, No. 10a pp. V42-V46 (1976). A similar method and computer controlled apparatus is described in EP 0079726B (Wiggins Teape). More recently, an apparatus has become available which is adapted for the measurement of streaming potential and/or the simultaneous measurement of both streaming potential and zeta potential. This apparatus is described in the European application 0462703 A1. It is an object of the invention to further develop said apparatus to make it applicable for the continuous, accurate and simultaneous on-line calculating and monitoring of both specific filtration resistance and zeta potential. According to the invention the above mentioned apparatus is characterized in that it further comprises means for measuring the height of the liquid-air interface on the screen side of the pad which is formed between two electrodes of the apparatus and that the means for processing the measurement values taken is adapted for the continuous, accurate and simultaneous on-line calculating and monitoring of both specific filtration resistance and zeta-potential of the solid material using the measurements taken. The apparatus of the invention makes possible a method for the continuous and accurate measuring and monitoring of both the streaming potential and specific filtration resistance of a fibrous dispersion in a fluid. The method comprises passing the fluid through a screen until a pad of the solid material is formed on the screen, maintaining the pressure on the screen side of the pad at a known value with respect to the pressure on the opposing side of the pad (that is the pressure difference across the screen and pad) measuring the temperature of the fluid, measuring the height of the liquid-air interface on the screen side of the pad, and simultaneously calculating both the streaming potential and specific filtration resistance from the measurements taken. Further details of the invention are mentioned in sub-claims 2 to 7. The procedure of determining both SFR and streaming potential simultaneously is a breakthrough and is believed to be novel. The invention will now be described with reference to the following drawings. Figure 1 is a graph depicting the increase in volume of liquid with the height in inches in the exit chamber after the pad formation screen. Figure 2 is a graph depicting the least square fit to data to obtain specific filtration resistance. Figure 3 is a graph showing the correlation of Schopper Riegler Freeness (SR) and specific filtration resistance (SFR). Figure 4 is a plot showing the correlation of maximum drainage to Schopper Riegler Freeness. Figure 5 is a graph depicting the correlation of specific filtration resistance and maximum drainage. Figure 6 depicts the influence of polymer addition on streaming potential. Figure 7 is a graph showing the influence of polymer addition on drainage. Figure 8 is a partial cross-sectional view of a measuring cell. Figures 9-12 represent printouts of drainage and zeta potential graphs, their overlay and logfile. Figure 13 is a graph depicting the influence of zeta potential on the microparticulate process. Figure 14 is a graph showing the combined effect on zeta potential and drainage. As indicated above, the operating principle is that a vacuum is applied and furnish is drawn to the screen to form a pad. White water is drawn through the pad while measuring the electrical potential across the pad. This electrical potential is the streaming potential. Through use of the appropriate equations this potential can be related to the zeta potential of the fiber. The amount of white water drawn through the screen and pad is monitored as a build up in height in the measuring chamber. This enables one to determine the volume drained as a function of time. The conductance and temperature are also monitored. All data is electronically recorded and stored in a microcomputer. The microcomputer also operates all functions of the instrument including either communications with a printer and a computer which enables operator input of several parameters and output of data, or output to a Distributed Control System which can adjust chemical feed rates in order to continuously optimize the process. An ultrasonic transducer was added to the instrument described in EP-A-462 703 together with supporting electronics so as to provide a sensor module as shown in Figure 8 which was then used to determine the height of the liquid-air interface in the exit chamber after the pad formation screen. The height of the liquid-air interface was determined with an accuracy of ± 0,0254 mm (0,001 inch). This height was translated into a volume drained by the correlation shown in figure 1. The height versus time data was automatically recorded and stored in the computer. This data was printed out and processed by software which transformed the data to volume. Measuring of the vacuum on the screen and pad sides is effected by a pressure transducer with an accuracy of ± 6.89 Pa (0,001 psi). Any deviation in vacuum from the norm is corrected after each measurement and thereby contributes to the high degree of precision of the method. Specific filtration resistance was therefore assessed by measuring the progressive increase in volume of liquid above the pad over a period of time. The lower the specific filtration resistance, the better the drainage on the paper wire machine. As indicated, the total volume of liquid which passes through the pad was measured to three digits, and expressed as "drainage in milliliters". Table 1 below is an example of the transformation for the Schopper Riegler 50 conditions with no polymer addition. The total drainage resistance, which is a function of the flow pattern and stock composition, is the sum of the effects of resistance to the flov imposed by the wire and by the fiber mat. Thus, the filtration equation can be written: dv/d = AdP/[µ (R f +R w )] where dv/d = drainage flow rate, m 3 /s A = cross section of the flow, m 2 dP = pressure gradient, Pa µ = filtrate viscosity, Pa*s R f = drainage resistance due to the fiber web, m -1 R w = drainage resistance due to the wire, m -1 The fiber resistance, R f , can be written in terms of the mass of fiber deposited on the web per unit area and a SFR coefficient: R f = (W/A)SFR where W = mass of the fiber web, kg A = area of the deposited fiber, m 2 SFR = specific filtration resistance, m/kg For a given instant , the mass of fiber in the web is W = CV§ Where C = concentration of fibers in the slurry, kg/m 3 V = volume of slurry already drained, m 3 § = fraction of stock retained. Thus, in incremental form, the combination and simplification of Eqs. 1, 2, and 3 yields in inverted form: Δ/Δ §CV(SFR)/(A 2 ΔP)+µR w /(AΔP) where Δ = time interval to filtrate the volume ΔV = filtrate volume, m 3 ΔP = pressure difference across the fiber mat and wire, Pa A = cross section of the fiber mat, m 2 C = fiber concentration in the slurry, kg/m 3 V = accumulated volume, m 3 µ = fluid viscosity, Pa*s §. = retention. If Eq. 4 is valid for the flow through the fiber mat and wire, then a graph of the ratio Δ/ΔV as a function of the accumulated volume V should result in a straight line. Experiments performed during this work showed that a linear relationship can be used to describe the measured points, as assumed. The slope and the intercept of the line are used to evaluate the SFR and the wire resistance, respectively. A special sensor was added to the Zeta Data to determine the height of the liquid interface in the exit chamber after the pad formation screen. This height was translated into a volume drained by the correlation shown in figure 1. The height vs. time data was automatically recorded and stored in the computer. This data was printed out and manually processed by a software algorithm which transformed the data to volume, the change in volume and then to the reciprocal of change in volume per time. This is the transformation necessary to use the theory described above. Table 1 is an example of this transformation for the Shopper Riegler 50 condition with no polymer addition. This data was then plotted in appropriate form and a least squares fit line applied to the data. This is shown in figure 2 and is representative of most data observed in this study. The theoretical model seems to be a good fit to the data and this was found over the complete range of data collected in this study. The Specific Filtration Resistance is obtained from the slope-m. SFR = mA 2 ΔP µ§C A = area m 2 µ = viscosity PASCAL sec C = concentration, kg/m 3 § = retention m = slope, ΔP = 4.13 x 10 4 Pa A = 1.266 x 10 4 m 2 C = 2 kg/m 3 § = 0.8 µ = 6.56 x 10 -4 Pa sec. SFR = m x .126 x 10 10 m/kg m = 2.57 sec/ml 2 SFR = 6.46 x 10 9 m/kg Since the procedure looked good, a study was designed to see if the SFR calculated by the procedure made sense and behaved in a manner which was consistent with papermaker's knowledge of the system. The Streaming Potential, SR, SFR and maximum drainage were determined for all samples tested. The maximum drainage is the volume drained at the end of the measurement cycle and is a quick indication of how the stock will drain. Table 2 is a summary of the results for the pure pulp samples where no polymer was added. The measurements all show the expected trend. Figure 3 illustrates the relationship between Schopper Riegler Freeness and Specific Filtration Resistance. As expected they track each other but do not correlate to each other in a linear fashion. They are distinctly different measurements with much more useful information obtainable from SFR since it has a theoretical base. Figure 4 shows the relationship which the maximum drainage number has with the Schopper Riegler Freeness parameter. Again they track each other but are different measurements. Figure 5 shows the relationship of maximum drainage to Specific Filtration Resistance and again a curve results. One might think that there was just a difference in device used to monitor, and Maximum Drainage and SFR should linearly correlate. Maximum Drainage and Schopper Riegler Freeness are merely qualitative measures of stock drainage. While they do qualitatively relate to how a stock will drain on a paper machine, they cannot quantitatively predict machine performance; only SFR has this capability. Since they are all intended to monitor the same phenomena, and they do track each other, it seems reasonable to shift to the new parameter, SFR, which has a theoretical basis. Table 3 summarizes the changes which happen to the 50 SR sample when subjected to various doses of Cypro 516. The polymer has sufficient effect on drainage to be equivalent to a shift in one level of refining chosen in this study. Figure 6 shows the stocks' response to polymer, as far as streaming potential is concerned; the expected patterns of increase to a more positive state of charge is observed. As expected, the cationic polymer neutralizes the negative charges on the cellulose and then makes the pulp positively charged. The effect one might expect on drainage would be low drainage when the fines are dispersed, then good drainage close to the positive side zero charge . Figure 7 shows what happens to the different drainage parameters. All three of the drainage parameters which were monitored go through an optimum. The optimum for SFR occurs before the optimum for SR freeness and Maximum Drainage. The optimum for SFR is also much more sharply defined than for SR freeness. All of the optimas occur before zero streaming potential occurs. There can be no conclusion drawn as to which measurement actually best picks optimum drainage, since the stock was not run on a machine. It appears that the minimum point for SR freeness and maximum drainage are very close so this questions will be answered when data is accumulated on machine with the Zeta Data. The patterns observed for the Maximum Drainage number are more consistent than the SR freeness patterns so the technique may be more sensitive. The SR freeness values often did not change with polymer addition and this was attributed to sensitivity. Table 4 gives the individual SFR individual measurements taken during the polymer study. All SFR data was calculated from duplicates. The standard deviation calculated from the average range is 0.14. Thus a confidence interval for measurement of two standard deviations would be 0.28. Therefore, the procedure is reproducible and reasonably sensitive. TRANSFORMATION OF DATA FOR SR 50 (NO POLYMER CONDITION) TIME HEIGHT VOLUME DELTA VOL 1/DV/DT 1 1.000 0.117 3.233 0.233 2 2.000 0.350 5.208 0.295 3 3.000 0.645 10.350 0.089 11.236 4 4.000 0.734 12.481 0.064 15.625 5 5.000 0.798 14.179 0.052 19.231 6 6.000 0.850 15.662 0.045 22.222 7 7.000 0.895 17.019 0.039 25.641 8 8.000 0.934 18.250 0.034 29.412 9 9.000 0.968 19.366 0.032 31.250 10 10.000 1.000 20.452 0.028 35.714 11 11.000 1.028 21.431 0.027 37.037 12 12.000 1.055 22.400 0.025 40.000 13 13.000 1.080 23.319 0.023 43.478 14 14.000 1.103 24.183 0.024 41.667 15 15.000 1.127 25.104 0.020 50.000 16 16.000 1.147 25.887 0.021 47.619 17 17.000 1.168 26.723 0.019 52.632 18 18.000 1.187 27.493 0.017 58.824 19 19.000 1.204 28.192 0.019 52.632 20 20.000 1.223 28.984 0.096 21 21.000 1.319 33.177 This data was then plotted in appropriate form and a least square fit line applied to the data. This is shown in Figure 2 and is representative of most data observed in this study. The theoretical model is a good fit to the data. The specific filtration resistance is obtained from the slope-m. Since the main papermaking variables which affect the way a stock drains are its degree of refining and the chemical additives introduced into the furnish, a study was designed to determine if the SFR calculated by the procedure made sense and behaved in a manner which was consistent with the paper maker's knowledge of the system. In this study plan, a bleach hardwood kraft pulp from the Champion Paper Company mill in Quinnesect, Michigan, was refined from 19 SR to 48 SR with samples taken at 19, 24, 32, 37 and 48 SR. This provided a wide range of freeness over which to test the procedure. The stock samples of different freeness were then treated with Cypro 516, a high charge density low molecular weight polyquaternary amine (produced by Cytec, a Division of the American Cyanamid Corporation), dosages of .005% from zero to .06% by weight of the stock. The samples were then run through the instrument on a batch basis in a recirculating mode. The data for the no polymer condition and the data for the various polymer addditions to the SR 50 stock were then evaluated. The streaming potential, SR, SFR and maximum drainage were determined for all samples tested. The maximum drainage is the volume drained at the end of the measurement cycle and is a quick indication of how the stock will drain. Table 2 is a summary of the results for the pure pulp samples where no polymer was added. The measurements all show the expected trend. SUMMARY OF RESULTS FOR PURE PULP SR MAX DRAIN SFR x 10 9 ZETA 1 19.000 108.400 0.650 0.000 2 24.000 79.300 1.300 0.000 3 32.000 57.200 3.640 -0.900 4 37.000 50.500 5.680 -0.165 5 48.000 42.600 6.700 -2.150 Figure 3 illustrates the relationship between Scopper Riegler Freeness and specific filtration resistance. As expected they track each other but do not correlate to each other in a linear fashion. They are distinctly different measurements with much more useful information obtainable from SRF since it has a theoretical basis. Figure 4 shows the relationship which the maximum drainage number has with the Schopper Riegler Freeness parameter. Again, they track each other but are different measurements. Figure 5 shows the relationship of maximum drainage to specific filtration resistance and again a curve results. One might think that there was just a difference in the device used to monitor, and maximum drainage and SFR should correlate linearly. Schopper Riegler Freeness is merely a qualitative measure of stock drainage. While it does qualitatively relate to how a stock will drain on a paper machine, it cannot quantitatively relate to how a stock will drain on a paper machine, it cannot quantitatively predict machine performance; only SFR has this capacity. Since Schopper Riegler Freeness and SFR are both intended to monitor the same phenomena, and they do track each other, it seems reasonable to shift to the new parameter, SFR, which has a theoretical basis. Table 3 summarizes the changes which happen to the 50 SR sample when subjected to various doses of Cypro 516. The polymer has sufficient effect on drainage to be equivalent to a shift in one level of refining chosen in this study. SUMMARY OF RESULTS FOR POLYQUATERNARY AMINE ADDITION Polyquaternary amine % SFR Drainage SR Freeness Streaming Potential 1 0.000 6.700 38.600 48.000 - 4.810 2 0.005 5.420 38.600 48.000 - 4.230 3 0.010 5.600 40.200 45.000 - 3.780 4 0.015 5.100 40.900 44.000 - 3.780 5 0.020 5.180 41.200 43.000 - 3.390 6 0.025 4.780 42.000 42.000 - 2.950 7 0.030 4.670 42.100 41.000 - 2.730 8 0.035 5.160 42.600 40.000 - 2.150 9 0.040 5.110 41.900 40.000 - 1.160 10 0.045 5.140 41.700 41.000 - 0.190 11 0.050 5.230 41.400 42.000 0.730 12 0.055 5.220 41.000 42.000 1.730 13 0.060 5.300 40.600 42.000 3.320 Figure 6 shows the stock's response to polymer, as far as streaming potential is concerned; the expected patterns of increase to a more positive state of charge is observed. As expected, the cationic polymer neutralizes the negative charges on the cellulose and then makes the pulp positively charged. The effect one might expect on drainage would be low drainage when the fines are dispersed, then good drainage around the positive side close to zero charge. Figure 7 shows what happens to the different drainage parameters. All three of the drainage parameters which were monitored go through an optimum. The optimum for SFR occurs before the optimum for SR freeness. The optimum for SFR is also much more sharply defined that for SR freeness. All of the optima occur before zero streaming potential occurs. There can be no conclusion drawn as to which measurement actually best picks optimum drainage, since the stock was not run on a machine. It appears that the minimum point for SR freeness and minimum SFR are very close so this question will be answered when data is accumulated on-machine. The patterns observed for the minimum SFR number is more consistent than the SR freeness patterns so the technique may be more sensitive. The SR Freeness values often did not change with polymer addition and this was attributed to lack of sensitivity. Table 4 gives the individual SFR measurements taken during the polymer study. All SFR data was calulated from duplicates. The standard deviation calculated from the average range is 0.14. Thus, a confidence interval for measurement of two standard deviations would be 0.28. Therefore, the procedure is reproducible and reasonably sensitive. Figure 8 is a cross-sectional view of the sensor module used for the determination of specific filtration resistance. The module is comprised of, in combination, tubing connector (1) for rinse water, tubing (2) and tubing connector (3), pneumatic tubing connetor (4), O-ring (5), alignment pin (6), chamber top (7), clamp (8), tubing connector (9) for rinse nozzle connection, rinse nozzle (10), clamp support (11), chamber upper tube (12), chamber center assembly screw (13), chamber upper section (14), screen (15), electrodes (16), electrode spacer (17), drainage measuring device (18), O-ring (19), chamber base (20), clamp support mounting screw (21), clamp mounting screw (22), chamber lower tube (23) and chamber lower section (24). In a typical experiment dry pulp was repulped in a Waring type blender in the laboratory, and adjusted to an appropriate consistency with tap water. Thirty liters of the furnish is transferred to a stainless steel vessel, equipped with an agitator. The contents of the vessel are circulated through the manifold which supplies the Sensor module of Figure 8 with furnish. Typically, a cationic organic chemical is added, followed after a specified delay, by an anionic inorganic microparticle. Unsing the system software, the zeta potential in millivolts is plotted, as is the drainage. In a specific example, 30 liters of furnish were prepared of bleached HWD:SWD at 0.5% consistency (150 g ) to which 0.125% PCC was added (37.5 g ). Next, 0.25% quaternary amine (1% concentration) was added (46.9 ml). Following a ten minute delay, 1% bentonite (5% dispersion) was added (37.5 ml). Figures 9, 10, 11 and 12 represent the respective printouts of the 060392B.LOG drainage and zeta potential graphs, their overlay and the logfile. Figure 11 shows the influence of the two additives on the zeta potential. It has been noted that the zeta potential just prior to the addition of microparticle should be slightly positive. If it is more than about +2 mV, the anionic microparticle is partly wasted in charge neutralization rather than forming a microflocculation structure, and efficiency can drop by about half. Should the charge be as negative as -5 mV prior to microparticle addition, efficiency can drop by half again. Maximizing drainage is key to the success of the microparticlate process because it ensures that retention and formation are also maximized. Figure 13,"The Influence of Zeta Potential on the Microparticulate Process" describes the incremental addition of a polyquaternary amine to an alkaline papermaking furnish, followed by the addition of an amount of colloidal silica proportional to the amount of polyquat. It is noted that in this particular case one needs to operate in the range of +2 to +4 mV zeta potential to maximize drainage. If the proportion of silica to polyquat is increased, the optimum zeta potential range becomes increasingly negative. An investigation was also made of the effect of adding wet strength resin and a microparticle to a laminate paper furnish with 50% headbox ash, at 1% consistency. the experiment depicted four drainage states. Figure 14 shows the combined effect on zeta potential and drainage. The first 2% increment of wet strength resin moved the zeta potential from -10 mV to 0 mV; the drainage improved from about 14 ml to 18 ml. The second 2% increment of wet strength resin moved the zeta potential; from about -4 mV to +4 mV, for a net change of zero and no change in drainage. The third 1.5% increment of wet strength resin moved the zeta potential frim +2 mV to +6 mV. As the zeta potential became more positive, the drainage decreased from 22 ml to 19 ml. Finally, the microparticulate process was invoked by adding 2.5% bentonite, which caused the zeta potential to drop from +5 mV to 0 mV, causing a large increase in drainage, from 19 to 29 ml. By the present invention there is provided a new, realistic, reproducible, continuous way to monitor specific filtration resistance. Although the invention has been illustrated by the foregoing, it is not to be construed as being limited to the materials disclosed therein, but rather, the invention is directed to the generic area as hereinbefore disclosed. Various modifications of the invention can be made without departing from the scope of the attached claims.

Claims: An apparatus for the continuous repetition of measurement cycles comprising means for passing a fluid containing solid material to a screen (15) to form a pad of solid material on the screen (15), pressure regulating means for measuring and maintaining the pressure difference across the pad and screen (15) at a predetermined value, means for measuring the temperature and conductance of the fluid and means for processing the measurements taken characterized in that the apparatus further comprises means for measuring the height of the liquid-air interface on the screen side of the pad, the pad is formed between two electrodes (16) of the apparatus and the means for processing the measurement values taken in adapted for the continuous, accurate and simultaneous on-line calculating and monitoring of both specific filtration resistance and zeta potential of the solid material using the measurements taken. The apparatus of claim 1, wherein the means for measuring the height of the liquid interface uses ultrasonic measurement means. The apparatus of claim 1, wherein the computation means is a microprocessor. The apparatus of claim 1, wherein the means for measuring the height of the liquid interface is accurate to 0,0254 mm (0,001 inch). The apparatus of claim 1, wherein the means for measuring the height of the liquid interface includes an ultrasonic transducer. The apparatus of claim 1, wherein the means for measuring pressure is accurate to 6.89 Pa (0,001 psi). The apparatus of claim 6, wherein the means for measuring pressure is a pressure transducer.

Inventors: PENNIMAN JOHN GRISCOM, PENNIMAN, JOHN GRISCOM
Applicants: PENNIMAN JOHN GRISCOM, PENNIMAN, JOHN GRISCOM
Application year: 1994
Main classification: G01N11
IPC codes: D21G9, G01N33, G01N11, G01N15, D21H23